Electronic circuit, module, and system

ABSTRACT

A convenient electronic circuit in which a switch is able to be switched through electric power obtained using weak radio waves is provided. An electronic circuit includes a switch which is connected between a power supply configured to output direct current (DC) electric power and a load driven through DC electric power supplied from the power supply and which switches a connection state between the power supply and the load from a non-conduction state to a conduction state; a power conversion circuit which includes a power input terminal to which electric power obtained through radio waves received by an antenna is input and a DC power output terminal configured to output DC electric power and which converts electric power input to the power input terminal into DC electric power and outputs the converted DC electric power from the DC power output terminal; and a control circuit configured to control a connection state of the switch to be in a conduction state when the power conversion circuit outputs DC electric power. The power conversion circuit includes at least a first capacitor, a first diode, a second capacitor, and a second diode.

RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2020-036248, filed on Mar. 3, 2020, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an electronic circuit, a module, and a system.

2. Description of the Related Art

In the related art, in electronic keys used for key systems for vehicles, electronic keys communicate with the vehicles when batteries built into the electronic keys are connected to control circuits using the electric power obtained using the radio waves from the vehicles. Techniques for minimizing the consumption of batteries in a standby state by cutting off the connection between batteries and circuits again if electronic keys are distant from vehicles (that is, during standby) are known (for example, refer to Patent Document 1)

PATENT DOCUMENTS

[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2011-24332

SUMMARY OF THE INVENTION

In the related art as described above, an analog front-end circuit (AFE) inside an electronic key is started up using electric power obtained by radio waves from a vehicle. At this time, the AFE is started up using electric power obtained by radio waves from a specific apparatus provided in the vehicle or the like.

However, when the AFE is tried to be started up using radio waves from the vehicle, the electronic key has a problem that it takes time to store electric power required for starting up the AFE. That is to say, it is inconvenient to have to keep the electronic key close to a position in which the electronic key can receive radio waves from the vehicle until the electronic key is started up.

The present invention was made in view of such circumstances, and an object of the present invention is to provide a convenient electronic circuit in which a switch can be switched using electric power obtained by weak radio waves.

An electronic circuit according to an aspect of the present invention includes a switch which is connected between a power supply configured to output direct current (DC) electric power and a load driven through DC electric power supplied from the power supply and which switches a connection state between the power supply and the load from a non-conduction state in which the supply of electric power from the power supply to the load is cut off to a conduction state in which electric power is supplied from the power supply to the load; a power conversion circuit which includes a power input terminal to which electric power obtained through radio waves received by an antenna capable of receiving radio waves is input and a DC power output terminal configured to output DC electric power and which converts electric power input to the power input terminal into DC electric power and outputs the converted DC electric power from the DC power output terminal; and a control circuit which includes an input terminal connected to the DC power output terminal of the power conversion circuit and an output terminal connected to the switch and configured to control a connection state of the switch and controls the connection state of the switch such that it is in a conduction state when the power conversion circuit outputs DC electric power due to the reception of radio waves by the antenna, wherein the power conversion circuit includes at least a first capacitor including a first electrode and a second electrode connected to the power input terminal, a first diode having an anode connected to a ground point and a cathode connected to the second electrode of the first capacitor, a second capacitor including a first electrode connected to the DC power output terminal and a second electrode connected to a ground point, and a second diode having an anode connected to the input terminal via a capacitor and a cathode connected to a first electrode of the second capacitor.

In an electronic circuit according to an aspect of the present invention, the power conversion circuit may further include a third capacitor including a first electrode and a second electrode connected to a ground point; a third diode having an anode connected to a second electrode of the first capacitor and a cathode connected to the first electrode of the third capacitor; a fourth capacitor including a first electrode and a second electrode connected to the power input terminal; and a fourth diode having an anode connected to a connection point between the first electrode of the third capacitor and the cathode of the third diode and a cathode connected to the second electrode of the fourth capacitor.

In an electronic circuit according to an aspect of the present invention, the power conversion circuit may further include; a fifth capacitor including a first electrode and a second electrode connected to a ground point; a fifth diode having an anode connected to the second electrode of the fourth capacitor and a cathode connected to the first electrode of the fifth capacitor; a sixth capacitor including a first electrode and a second electrode connected to the power input terminal; and a sixth diode having an anode connected to a connection point between the first electrode of the fifth capacitor and the cathode of the fifth diode and a cathode connected to the second electrode of the sixth capacitor.

Also, a module according to an aspect of the present invention includes: the electronic circuit described above; a power supply configured to output DC electric power; and a load driven through DC electric power supplied from the power supply.

A module according to an aspect of the present invention is accommodated in a waterproof housing.

Furthermore, a system according to an aspect of the present invention includes the module; and a transmitter configured to transmit prescribed radio waves to the module.

According to the present invention, it is possible to provide a convenient electronic circuit in which a switch can be switched using electric power obtained by weak radio waves.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a constitution of a latch system in an embodiment.

FIG. 2 is a diagram illustrating an example of a constitution of a latch module in a first embodiment.

FIG. 3 is a diagram illustrating a first modified example of the constitution of the latch module in the first embodiment.

FIG. 4 is a diagram illustrating an example of a constitution of a control circuit in the first embodiment.

FIG. 5 is a diagram illustrating a second modified example of the constitution of the latch module in the first embodiment.

FIG. 6 is a diagram illustrating an example of a housing with a waterproof structure in the first embodiment.

FIG. 7 is a diagram illustrating an example of a power conversion circuit in a second embodiment.

FIG. 8 is a diagram illustrating a first modified example of the power conversion circuit in the second embodiment.

FIG. 9 is a diagram illustrating a second modified example of the power conversion circuit in the second embodiment.

FIG. 10 is a diagram illustrating an example of a first antenna and a second antenna in a third embodiment.

FIG. 11 is a diagram illustrating an example of the first antenna and the second antenna in a third embodiment.

FIG. 12 is a diagram illustrating an example of a constitution of a latch module in the third embodiment.

FIG. 13 is a diagram illustrating a first modified example of the constitution of the latch module in the third embodiment.

FIG. 14 is a diagram illustrating a second modified example of the constitution of the latch module in the third embodiment.

FIG. 15 is a diagram illustrating a third modified example of the constitution of the latch module in the third embodiment.

FIG. 16 is a diagram illustrating a fourth modified example of the constitution of the latch module in the third embodiment.

FIG. 17 is a diagram illustrating a fifth modified example of the constitution of the latch module in the third embodiment.

FIG. 18 is a diagram illustrating an example of a housing with a waterproof structure in the third embodiment.

FIG. 19 is a diagram illustrating an example of a constitution of a latch system in a fourth embodiment.

FIG. 20 is a diagram illustrating a case in which a first antenna receives radio waves in an example of the constitution of the latch system in the fourth embodiment.

FIG. 21 is a diagram illustrating a case in which a second antenna receives radio waves in an example of the constitution of the latch system in the fourth embodiment.

FIG. 22 is a diagram illustrating an example of a constitution of a power detector in the fourth embodiment.

FIG. 23 is a diagram illustrating an example of a constitution of the power detector having gain switching in the fourth embodiment.

FIG. 24 is a diagram illustrating an example of a constitution of a circuit of the power detector having gain switching in the fourth embodiment.

FIG. 25 is a diagram illustrating an example of a housing with a waterproof structure in the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Constitution of Latch System 100]

A constitution of a latch system 100 will be described below with reference to the drawings.

FIG. 1 is a diagram illustrating an example of the constitution of the latch system 100 in an embodiment. As illustrated in FIG. 1, the latch system 100 includes a transmitter 70 and a latch module 1.

The transmitter 70 is a terminal in which radio waves can be transmitted. Here, for example, the radio waves are radio waves transmitted by a transmission-side device during wireless communication performed in accordance with a communication standard such as Bluetooth (registered trademark) or Wi-Fi (registered trademark). The radio waves are not limited to a communication standard such as Bluetooth (registered trademark) or Wi-Fi (registered trademark), various communication methods can be adopted for the radio waves, and the radio waves may be transmitted through communication according to a unique standard in which the default communication standard is not satisfied.

For example, the transmitter 70 is a mobile information processing terminal in which wireless communication is possible such as multifunctional mobile phone terminals (smartphones), mobile phone terminals, personal digital assistants (PDAs), notebook PCs, and tablet PCs. The transmitter 70 is not limited to a mobile information processing terminal and may be another information processing terminal.

In this example, the transmitter 70 transmits radio waves 71.

The latch module 1 includes a power supply 50, a load 60, and a latch circuit 10. The latch module 1 receives the radio waves 71 transmitted from the transmitter 70.

The power supply 50 is a power supply configured to output direct current (DC) electric power. For example, the power supply 50 is a battery such as a lithium battery. When the latch module 1 is a small-sized device, the power supply 50 may be a battery as installed in a board. The power supply 50 supplies electric power to the load 60.

The load 60 has functions such as communication functions. For example, the load 60 may include a read only memory (ROM) (not shown), a random access memory (RAM) (not shown), and a central processing unit (CPU) (not shown).

The latch circuit 10 is connected between the power supply 50 and the load 60. The power supply 50 supplies electric power to the load 60 via the latch circuit 10.

The latch circuit 10 receives the radio waves 71 transmitted from the transmitter 70. The latch circuit 10 receives the radio waves 71 transmitted from the transmitter 70 to control a conduction state between the power supply 50 and the load 60. Hereinafter, the latch circuit 10 is also referred to as an “electronic circuit.”

First Embodiment

A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram illustrating an example of a constitution of the latch module 1 in the first embodiment. In FIG. 2, the latch module 1 includes a latch circuit 10, a power supply 50, and a load 60.

The latch circuit 10 includes an antenna 140, a power conversion circuit 110, a control circuit 120, and a switch 130.

The antenna 140 is connected to the power conversion circuit 110. The antenna 140 receives radio waves 71 transmitted from a transmitter 70.

The power conversion circuit 110 includes a power input terminal 111 as an input terminal and a DC power output terminal 112 as an output terminal. Radio waves received by the antenna 140 are input to the power input terminal 111. The electric power obtained by the radio waves received by the antenna 140 is converted into DC electric power and output. The DC power output terminal 112 outputs the DC electric power converted by the power conversion circuit 110. That is to say, the power conversion circuit 110 includes the power input terminal 111 to which the electric power obtained by the radio waves received by the antenna 140 capable of receiving radio waves is input and the DC power output terminal 112 configured to output DC electric power. Furthermore, the power conversion circuit 110 converts the electric power input to the power input terminal 111 into DC electric power and the converted DC electric power is output from the DC power output terminal 112.

The power conversion circuit 110 may include an RF-DC conversion circuit 113 and a booster circuit 114.

The RF-DC conversion circuit 113 converts the electric power obtained by the radio waves input to the power input terminal 111 into DC electric power. The RF-DC conversion circuit 113 outputs the converted DC electric power to the booster circuit 114.

The booster circuit 114 steps up a voltage of the DC electric power converted by the RF-DC conversion circuit 113. The booster circuit 114 outputs the stepped-up electric power via the DC power output terminal 112.

The control circuit 120 includes an input terminal 121 connected to the DC power output terminal 112 of the power conversion circuit 110 and an output terminal 122 connected to the switch 130 and configured to control a connection state of the switch 130. The control circuit 120 includes a power supply terminal 123 as a power source terminal.

The DC electric power output by the power conversion circuit 110 is input to the input terminal 121. The output terminal 122 outputs an output signal corresponding to a state of the input terminal 121. Electric power is supplied from the power supply 50 to the power supply terminal 123.

The switch 130 is connected between the power supply 50 configured to output DC electric power and the load 60 driven through the DC electric power supplied from the power supply 50. The switch 130 switches a connection state between the power supply 50 and the load 60 from a non-conduction state to a conduction state.

The non-conduction state is a state in which the supply of electric power from the power supply 50 to the load 60 is cut off and the conduction state is a state in which electric power is supplied from the power supply 50 to the load 60.

In this example, the control circuit 120 includes a flip-flop 127. The flip-flop 127 switches a control signal output from the output terminal 122.

Although FIG. 2 illustrates an example in which a D flip-flop (a D-F/F) is utilized for the flip-flop 127, the D-F/F may be composed of another flip-flop such as a T flip-flop.

The control circuit 120 controls the conduction state of the switch 130. Specifically, the control circuit 120 controls the connection state of the switch 130 to be in a conduction state when the power conversion circuit 110 outputs DC electric power due to the antenna 140 receiving the radio waves 71.

More specifically, the input terminal 121 of the control circuit 120 is connected to a CLK terminal 1271 and a D terminal 1272 of the flip-flop 127. Furthermore, the output terminal 122 of the control circuit 120 is connected to a Q terminal 1273 of the flip-flop 127.

Since the input terminal 121 has a low level (the same potential as a ground potential) in a state in which the antenna 140 is not receiving the radio waves 71 (that is, in a state in which the transmitter 70 is distant from the latch circuit 10 or the radio waves 71 are not being transmitted from the transmitter 70), the Q terminal 1273 has the low level held therein. In this state, the switch 130 is controlled such that it is brought into a non-conduction state. That is to say, in this state, electric power is not supplied from the power supply 50 to the load 60.

The RF-DC conversion circuit 113 outputs DC electric power to the booster circuit 114 in a state in which the antenna 140 is receiving the radio waves 71 (that is, in a state in which the radio waves 71 are being transmitted from the transmitter 70 or the transmitter 70 is brought closer to the latch circuit 10). The booster circuit 114 performs stepping-up until the Q terminal 1273 of the flip-flop 127 has a changing threshold value potential or more. At this time, in the power conversion circuit 110, a potential sufficient to change a state of the Q terminal 1273 is input to the CLK terminal 1271 and the D terminal 1272 of the flip-flop 127. Thus, the level of the Q terminal 1273 is changed to a high level. In this state, the switch 130 is controlled to be in a conduction state.

If the switch 130 is controlled to be in a conduction state, the power supply 50 supplies electric power to the load 60 via the switch 130.

Since electric power is supplied from the power supply 50 to the flip-flop 127, even if the antenna 140 transitions to a state in which the antenna 140 does not receive the radio waves 71 (that is, a state in which the latch circuit 10 does not receive radio waves due to reasons such as the transmitter 70 moving to a position in which the transmitter is distance from the latch circuit 10), the Q terminal 1273 continues to output a high level.

In this embodiment, when the switch 130 is switched to be in a conduction state, the control circuit 120 keeps the switch 130 conductive using electric power supplied from the power supply 50 to the power supply terminal 123.

In this example, since the flip-flop 127 is connected to the power supply 50 via the power supply terminal 123, a constitution in which the flip-flop 127 with low power consumption is selected to significantly minimize an influence on a battery lifespan may be provided. For example, a flip-flop with low power consumption of less than 1 μA (microampere) may be selected.

FIG. 3 is a diagram illustrating a first modified example of the constitution of the latch module 1 in the first embodiment. A latch module 1 b illustrated in FIG. 3 is a first modified example of the latch module 1. A constituent element in the first modified example that is the same as the latch module 1 described above will be denoted by the same reference numeral and a description thereof will be omitted. The latch module 1 b is different from the latch module 1 described above in that the latch module 1 b includes a control circuit 120 b instead of the control circuit 120.

The control circuit 120 b includes an input terminal 121 b connected to a DC power output terminal 112 of a power conversion circuit 110 and an output terminal 122 b connected to a switch 130 and configured to control a connection state of the switch 130. Furthermore, the control circuit 120 b includes a power supply terminal 123 b as a power supply terminal.

DC electric power output by the power conversion circuit 110 is input to the input terminal 121 b. The output terminal 122 b outputs an output signal corresponding to a state of the input terminal 121 b. Electric power is supplied from a power supply 50 to the power supply terminal 123 b.

In this example, the control circuit 120 b includes a power detector 126. The power detector 126 includes a detection input terminal 1261, a reference input terminal 1262, and a voltage detection output terminal 1263 as input/output terminals. The reference input terminal 1262 is connected to a ground point TG. The voltage detection output terminal 1263 outputs a potential corresponding to a potential of the detection input terminal 1261 and a potential of the reference input terminal 1262.

In a state in which an antenna 140 does not receive radio waves 71 (that is, in a state in which a transmitter 70 is distance from a latch circuit 10 or radio waves 71 is not transmitted from the transmitter 70), the input terminal 121 b has a low level. Thus, the low level is input to the detection input terminal 1261. Since the reference input terminal 1262 is connected to the ground point TG (fixed to the low level), the voltage detection output terminal 1263 outputs the low level. In this state, the switch 130 is controlled to be in a non-conduction state.

In a state in which the antenna 140 is receiving radio waves 71 (that is, in a state in which radio waves 71 are being transmitted from the transmitter 70 or the transmitter 70 is brought closer to the latch circuit 10), an RF-DC conversion circuit 113 outputs DC electric power to a booster circuit 114. The booster circuit 114 steps up a potential of a power detector 126 to an operation potential (a high level) thereof. The power conversion circuit 110 outputs a high level. Since the high level is input to the detection input terminal 1261 of the power detector 126, the voltage detection output terminal 1263 outputs a high level. In this state, the switch 130 is controlled to be in a conduction state.

In this example, the detection input terminal 1261 of the power detector 126 is connected to the voltage detection output terminal 1263.

The control circuit 120 b may include a resistor 124 b. In this case, the detection input terminal 1261 of the power detector 126 is connected to the voltage detection output terminal 1263 via the resistor 124 b. As an example, a resistance value of the resistor 124 b may be 10 mega-ohms or more. When the control circuit 120 b includes the resistor 124 b, it is possible to further minimize power consumption.

When the power detector 126 outputs a high level to control the switch 130 to be in a conduction state and thus the power supply 50 is connected to a load 60, a current flowing through the control circuit 120 b only flows through the resistor 124 b and electric current consumption of the power detector 126, both of which are small.

In this way, since the power consumption of the power detector 126 is theoretically zero, the power consumption of the power supply 50 in which the switch 130 is in a non-conduction state can be changed to substantially zero. Therefore, in the example in which the power detector 126 is provided, it is possible to further reduce power consumption as compared with the example described above in which the flip-flop 127 is provided.

FIG. 4 is a diagram illustrating an example of a constitution of the power detector 126 in the first embodiment.

In FIG. 4, (A) is an example of the constitution of the power detector 126, and the power detector 126 includes a transistor Q1, a transistor Q2, a transistor Q3, a transistor Q4, an inverter 1264, and a resistor 1265.

The transistor Q1, the transistor Q2, and the transistor Q4 are enhancement elements. The transistor Q3 is a depression element.

When the output terminal 122 b outputs a low level, the transistor Q2 and the transistor Q3 are turned on. When the output terminal 122 b outputs a high level, the transistor Q1 and the transistor Q4 are turned on.

In this example, a current flows from the power supply terminal 123 b to the ground point TG through two routes. A first route is a route in which a current flows from the power supply terminal 123 b to the ground point TG via the transistor Q1 and the transistor Q3 and a second route is a route in which a current flows from the power supply terminal 123 b to the ground point TG via the transistor Q2 and the transistor Q4. The power detector 126 cuts off both of the routes in which a current flows from the power supply terminal 123 to the ground point TG all the time, regardless of the state of the output terminal 122 b.

Therefore, the power consumption of the power detector 126 is theoretically zero.

In FIG. 4, (B) is a truth value table for an example of the constitution of the power detector 126 illustrated in (A). (B) illustrates a correspondence relationship between potentials of the input terminal 121 b and the output terminal 122 b and states of the transistor Q1, the transistor Q2, the transistor Q3, and the transistor Q4.

IN indicates a level of the potential of the input terminal 121 b and OUT indicates a level of the potential of the output terminal 122 b. The transistor Q1, the transistor Q2, the transistor Q3, and the transistor Q4 indicate states of the transistors.

FIG. 5 is a diagram illustrating a second modified example of the constitution of the latch module 1 in the first embodiment. A latch module 1 c illustrated in FIG. 5 is the second modified example of the latch module 1. A constituent element in the second modified example that is the same as the latch module 1 described above will be denoted by the same reference numeral and a description thereof will be omitted. The latch module 1 c is different from that in a case in which a latch module 1 a and a latch module 1 b supply electric power to a power supply terminal 123 c included in a control circuit 120 c. The control circuit 120 c is an example of the control circuit 120.

The control circuit 120 c includes an input terminal 121 c connected to a DC power output terminal 112 of a power conversion circuit 110 and an output terminal 122 c connected to a switch 130 and configured to control a connection state of the switch 130. Furthermore, the control circuit 120 c includes the power supply terminal 123 c as a power supply terminal.

DC electric power output by the power conversion circuit 110 is input to the input terminal 121 c. The output terminal 122 c outputs an output signal corresponding to a state of the input terminal 121 c. Electric power is supplied from at least one of the power conversion circuit 110 and the power supply 50 to the power supply terminal 123 c.

In this example, the latch module 1 c includes a diode D1 and a diode D2. The diode D1 has an anode connected to the DC power output terminal 112 of the power conversion circuit 110 and a cathode connected to the power supply terminal 123 c of the control circuit 120 c. The diode D2 has an anode connected to a connection point between the switch 130 and the load 60 and a cathode connected to the power supply terminal 123 c of the control circuit 120 c. Hereinafter, the diode D1 will be also referred to as a “first diode” and the diode D2 will be also referred to as a “second diode.”

In a state in which the antenna 140 does not receive radio waves 71 (that is, in a state in which the transmitter 70 is distance from the latch circuit 10 or radio waves 71 are not transmitted from the transmitter 70), electric power is not supplied to the control circuit 120 c. In this case, the switch 130 is controlled to be in a non-conduction state. The output terminal 122 c may be fixed at a low level using a resistor (not shown) or the like.

In a state in which the antenna 140 is receiving radio waves 71 (that is, in a state in which radio waves 71 are being transmitted from the transmitter 70 or the transmitter 70 is brought closer to the latch circuit 10), an RF-DC conversion circuit 113 outputs DC electric power to the booster circuit 114. The booster circuit 114 steps up the DC electric power to a potential of a potential or more obtained by adding an amount corresponding to a stepped-down voltage of the diode D1 to an operation potential of the power detector 126. The power conversion circuit 110 supplies electric power from the DC power output terminal 112 to the power supply terminal 123 c of the control circuit 120 c via the diode D1.

In this case, a potential output from the DC power output terminal 112 of the power conversion circuit 110 is also input to the input terminal 121 c of the control circuit 120 c. If a high level is input to the input terminal 121 c, the control circuit 120 c outputs a high level to the output terminal 122 c. Therefore, the switch 130 is controlled to be in a conduction state.

If the switch 130 is controlled to be in the conduction state, the power supply 50 supplies electric power to the power supply terminal 123 c of the control circuit 120 c via the switch 130 and the diode D2.

Even if the antenna 140 does not receive radio waves 71 (that is, a state in which the latch circuit 10 no longer receives radio waves due to reasons such as the transmitter 70 moving distance from the latch circuit 10) transitions, the control circuit 120 c can receive the supply of electric power from the power supply 50 via the switch 130 and the diode D2.

Therefore, in this embodiment, in the switch 130, if the switch 130 is controlled to be in a conduction state when the antenna 140 receives the radio waves 71, the switch 130 is kept conductive.

FIG. 6 is a diagram illustrating an example of a housing with a waterproof structure in the first embodiment. As illustrated in FIG. 6, a latch waterproof module 2 includes the latch circuit 10, the power supply 50 configured to output DC electric power, the load 60 configured to be driven by DC electric power supplied from the power supply 50, and a housing 80.

The housing 80 includes the latch circuit 10, the power supply 50, and the load 60 accommodated therein. The housing 80 has waterproof performance.

Summary of Effects of the First Embodiment

According to the embodiment described above, the latch circuit 10 controls a connection state between the power supply 50 and the load 60 to be in a conduction state using the radio waves received by the antenna 140.

In the related art, in the small-sized device as shipped with the battery installed in the board, electric power is supplied the moment the battery is installed, and the consumption of the battery begins. Although it is desirable that electric power be supplied only after the device is delivered to a customer or when a customer intends to supply electric power in view of a battery lifespan, contact switches, (removable) insulating films, and the like lead to an increase in size of the small-sized device.

The latch circuit 10 can minimize an increase in size of the small-sized device by controlling a connection state between the power supply 50 and the load 60 to be in a conduction state using the radio waves received by the antenna 140.

Also, according to the above-described embodiment, in the latch circuit 10, the power conversion circuit 110 converts the electric power obtained by the radio waves received by the antenna 140 into DC electric power and the control circuit 120 controls a conduction state of the switch 130. Since the latch circuit 10 can switch a state of the switch 130 to be in a conduction state even using weak radio waves when including the control circuit 120, it does not take time to start up the AFE which is a load. Thus, it is possible to provide the latch module 1 in which it does not take time from the reception of radio waves to the starting-up of the load 60.

Therefore, it is possible to provide the convenient latch circuit 10.

Also, according to the above-described embodiment, the control circuit 120 included in the latch circuit 10 receives electric power supplied from the power supply 50. Therefore, after the antenna 140 receives radio waves, the latch circuit 10 can keep the connection state of the switch 130 conductive even in a state in which the antenna 140 does not receive radio waves.

Furthermore, according to the above-described embodiment, the control circuit 120 includes the flip-flop 127. Therefore, the control circuit 120 can switch and keep the connection state of the switch 130 using a simple constitution.

Also, according to the above-described embodiment, the control circuit 120 includes the power detector 126 having feedback.

Since the output signal of the control circuit 120 is fed back to the input, the control circuit 120 can maintain the connection state of the switch 130. Furthermore, it is possible to maintain the state of the switch 130 with low power consumption.

Furthermore, according to the above-described embodiment, the power detector 126 further includes the resistor 124 b in which 10 mega-ohms or more is provided. Therefore, when the control circuit 120 includes the resistor 124 b, it is possible to further minimize electric power consumed by the control circuit 120.

In addition, according to the above-described embodiment, when the latch module 1 includes the diode D1, the power conversion circuit 110 provides electric power of the control circuit 120. Therefore, the latch module 1 can obtain electric power for switching the switch 130 to a conduction state from radio waves received by the antenna 140. That is to say, the latch module 1 can switch the switch 130 to a conduction state without consuming electric power of the power supply 50.

Moreover, according to the above-described embodiment, when the latch module 1 includes the diode D2, after the switch 130 is controlled to be in a conduction state, it is possible to receive the supply of electric power from the power supply 50. Therefore, the switch 130 can maintain the conduction state.

In addition, according to the above-described embodiment, the latch module 1 is accommodated in the housing 80 with waterproof performance. For example, when the starting-up of the system is required in a non-contact state in a device used in a sealed state in water, it is possible to start up the system in a non-contact state by applying the latch module 1 in this embodiment.

Examples of the device used in a sealed state in water a water quality measurement device, a small-sized camera device, and the like. Furthermore, the expression “in water” includes not only water but also a wide range of liquids such as electrolytic solutions and body fluids.

Second Embodiment

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 7 is a diagram illustrating an example of a power conversion circuit 110 d in the second embodiment. The power conversion circuit 110 d is an example of the power conversion circuit 110.

In FIG. 7, the power conversion circuit 110 d includes a first capacitor C11, a first diode D11, a second diode D12, and a second capacitor C12.

The first capacitor C11 includes a first electrode C11 a and a second terminal C11 b. The first electrode C11 a of the first capacitor C11 is connected to a power input terminal 111 a and a second electrode C11 b is connected to a connection point between a cathode of the first diode D11 and an anode of the second diode D12.

The first diode D11 has an anode connected to a ground point TG and the cathode connected to the second electrode C11 b of the first capacitor C11.

The second capacitor C12 includes a first electrode C12 a and a second electrode C12 b. The first electrode C12 a of the second capacitor C12 is connected to the DC power output terminal 112 d and the second electrode C12 b is connected to the ground point TG.

The second diode D12 has an anode connected to a power input terminal 111 d via a capacitor. In the case of this example, the anode of the second diode D12 is connected to the power input terminal 111 d via the first capacitor C11. Furthermore, the second diode D12 has a cathode connected to the first electrode C12 a of the second capacitor C12.

If a positive potential is applied to the power input terminal 111 d, a current I11 flows from the power input terminal 111 d via the first capacitor C11 and the second diode D12. Electric charges are accumulated in the second capacitor C12 through the current Ill.

If a negative potential is applied to the power input terminal 111 d, a current I12 flows from the ground point TG via the first diode D11 and the first capacitor C11. Electric charges are accumulated in the first capacitor C11 through the current I12.

When a positive potential is applied to the power input terminal 111 d again, a current I11 flows from the power input terminal 111 d via the first capacitor C11 and the second diode D12. As a result, a potential twice that of the power input terminal 111 d is output to the DC power output terminal 112 d. This is an operation of a half-wave voltage doubler rectifier circuit.

The power conversion circuit 110 d is a voltage doubler rectifier circuit configured to step up weak radio waves. The weak radio waves uses, for example, a 2.4 GHz band such as a Bluetooth (registered trademark) low Energy (LE) (hereinafter referred to as a “BLE”) standard communication method installed in a smartphone or the like. It is desirable that the first diode D11 and the second diode D12 (hereinafter, when diodes provided in the power conversion circuit 110 are not distinguished, they are referred to as a “diode D”) have excellent high frequency characteristics, a low forward voltage, and a small capacitance between terminals. In this example, the diode D may be a Schottky barrier diode.

In the first capacitor C11 and the second capacitor C12 (hereinafter, when capacitors provided in the power conversion circuit 110 are not distinguished, they are referred to as a “capacitor C”), a response rate and an arrival voltage value of a stepped-up voltage change in accordance with a capacitance. Furthermore, if the capacitor C does not have a sufficient capacitance value, an amount of ripple (an amount of voltage fluctuation) of an output voltage increases and DC characteristics deteriorate. On the other hand, if the capacitor C has a too large capacitance value, it takes time to charge and responsiveness deteriorates.

Therefore, the capacitance value of the capacitor C is adjusted to a value at which well-balanced and good voltage doubler characteristics can be obtained for each application of the selected diode D and latch circuit 10. For example, in this embodiment, 33 pF, 24 pF, and the like are preferable at 2.4 GHz.

An optimum capacitance value changes depending on a stray capacitance, a board pattern, an installation layout, and the like of a board. In the circuit illustrated in FIG. 7, an optimum value changes in the range of several to several tens of pF. An optimum capacitance value needs to be confirmed in accordance with a stray capacitance, a board pattern, an installation layout, and the like of a board.

When the power conversion circuit 110 has a constitution in which the above-described voltage doubler rectifier circuit is incorporated in multiple stages, it is possible to obtain a potential at which the control circuit 120 can operate even with weaker radio waves.

FIG. 8 is a diagram illustrating the power conversion circuit 110 e which is a first modified example of the power conversion circuit 110 in the second embodiment. The power conversion circuit 110 e is an example of the power conversion circuit 110 described above. A constituent element in the first modified example that is the same as the power conversion circuit 110 described above will be denoted by the same reference numeral and a description thereof will be omitted.

In FIG. 8, a power conversion circuit 110 e includes a first capacitor C21, a first diode D21, a second capacitor C22, a second diode D22, a third capacitor C23, a third diode D23, a fourth capacitor C24, and a fourth diode D24.

In this example, the first capacitor C21, the first diode D21, the second capacitor C22, and the second diode D22 are the same as the first capacitor C11, the first diode D11, the second capacitor C12, and the second diode D12, respectively.

When the power conversion circuit 110 e further includes the third capacitor C23, the third diode D23, the fourth capacitor C24, and the fourth diode D24 as compared with the power conversion circuit 110 d, a two-stage voltage doubler rectifier circuit is constituted.

The third capacitor C23 includes a first electrode C23 a and a second electrode C23 b. The first electrode C23 a of the third capacitor C23 is connected to a cathode of the third diode D23 and the second electrode C23 b is connected to a ground point TG.

The third diode D23 has an anode connected to a second electrode C21 b of the first capacitor C21 and the cathode connected to the first electrode C23 a of the third capacitor C23.

The fourth capacitor C24 includes a first electrode C24 a and a second electrode C24 b. The first electrode C24 a of the fourth capacitor C24 is connected to a power input terminal 111 e and the second electrode C24 b is connected to a cathode of the fourth diode D24.

The fourth diode D24 has an anode connected to a connection point between the cathode of the third diode D23 and the first electrode C23 a of the third capacitor C23 and the cathode connected to the second electrode C24 b of the fourth capacitor C24.

Also, in the case of this example, the anode of the second diode D22 is connected to the power input terminal 111 e via the fourth capacitor C24.

In the example illustrated in FIG. 8, a voltage four times an input voltage input to the power input terminal 111 e can be output from the DC power output terminal 112 e.

When the multi-stage voltage doubler rectifier circuit is constituted in this way, the power conversion circuit 110 can obtain a potential at which the control circuit 120 can operate.

Here, when the multi-stage voltage doubler rectifier circuit is constituted, it causes a decrease in RF-DC conversion efficiency. Furthermore, the manufacturing cost increases due to an increase in the number of parts constituting the multi-stage voltage doubler rectifier circuit. Therefore, it is desirable to set the number of stages appropriate for each application.

FIG. 9 is a diagram illustrating a power conversion circuit 110 f which is a second modified example of the power conversion circuit 110 in the second embodiment. The power conversion circuit 110 f is an example of the power conversion circuit 110 described above. A constituent element in the second modified example that is the same as the power conversion circuit 110 described above will be described by the same reference numeral and a description thereof will be omitted.

In FIG. 9, the power conversion circuit 110 f includes a first the capacitor C31, a first diode D31, a second capacitor C32, a second diode D32, a third capacitor C33, a third diode D33, a fourth capacitor C34, a fourth diode D34, a fifth capacitor C35, a fifth diode D35, a sixth capacitor C36, and a sixth capacitor C36.

In this example, the first the capacitor C31, the first diode D31, the second capacitor C32, the second diode D32, the third capacitor C33, the third diode D33, the fourth capacitor C34, and the fourth diode D34 are the same as the first capacitor C21, the first diode D21, the second capacitor C22, the second diode D22, the third capacitor C23, the first diode D23, the fourth capacitor C24, and the fourth diode D24, respectively.

The power conversion circuit 110 f further includes a fifth capacitor C35, a fifth diode D35, a sixth capacitor C36, and a sixth diode D36 compared with the power conversion circuit 110 e to constitute a three-stage voltage doubler rectifier circuit.

The fifth capacitor C35 includes a first electrode C35 a and a second electrode C35 b. The first electrode C35 a of the fifth capacitor C35 is connected to a cathode of the fifth diode D35 and the second electrode C35 b is connected to the ground point TG.

The fifth diode D35 has an anode connected to a second electrode C34 b of the fourth capacitor C34 and the cathode connected to the first electrode C35 a of the fifth capacitor C35.

The sixth capacitor C36 includes a first electrode C36 a and a second electrode C36 b. The first electrode C36 a of the sixth capacitor C36 is connected to a power input terminal 111 f and the second electrode C36 b is connected to a cathode of the sixth diode D36.

The sixth diode D36 has an anode connected to a connection point between the cathode of the fifth diode D35 and the first electrode C35 a of the fifth capacitor C35 and the cathode connected to the second electrode C36 b of the sixth capacitor C36.

Also, in the case of this example, the anode of the second diode D32 is connected to the power input terminal 111 f via the sixth capacitor C36.

In the example illustrated in FIG. 9, a voltage which is six times an input voltage input to the power input terminal 111 f can be output from the DC power output terminal 112 f.

When the multi-stage voltage doubler rectifier circuit is constituted in this way, the power conversion circuit 110 can obtain a potential at which the control circuit 120 can operate. In the example associated with the power conversion circuit 110 f, the control circuit 120 can be operated by weaker radio waves as compared with the example associated with the power conversion circuit 110 e.

Summary of Effects of Second Embodiment

According to the embodiment described above, the latch circuit 10 illustrated in FIG. 1 constitutes the power conversion circuit 110 using the voltage doubler rectifier circuit. When the latch circuit 10 constitutes the power conversion circuit 110 using the voltage doubler rectifier circuit, it is possible to generate DC electric power stepped-up from that of weak radio waves. The power conversion circuit 110 can drive the control circuit 120 by supplying the stepped-up DC electric power to the control circuit 120.

Also, according to the above-described embodiment, the voltage doubler rectifier circuit is constituted of the capacitor C and the diode D. Therefore, the latch circuit 10 can constitutes the power conversion circuit 110 with a simple constitution.

Furthermore, according to the above-described embodiment, the latch circuit 10 constitutes the power conversion circuit 110 using the two-stage voltage doubler rectifier circuit. When the latch circuit 10 constitutes the power conversion circuit 110 using the two-stage voltage doubler rectifier circuit, it is possible to drive the control circuit 120 even with weak radio waves. When the latch circuit 10 drives the control circuit 120 even with weak radio waves, it is possible to control the power supply 50 and the load 60 to be in a conduction state.

In addition, according to the above-described embodiment, the latch circuit 10 constitutes the power conversion circuit 110 using the three-stage voltage doubler rectifier circuit. When the latch circuit 10 constitutes the power conversion circuit 110 using the three-stage voltage doubler rectifier circuit, it is possible to drive the control circuit 120 even with weaker radio waves compared with the two-stage voltage doubler rectifier circuit. The latch circuit 10 can control the power supply 50 and the load 60 to be in a conduction state by driving the control circuit 120 even with weaker radio waves.

Third Embodiment

A third embodiment of the present invention will be described below with reference to the drawings.

FIG. 10 is a diagram illustrating an example of a first antenna 240 and a second antenna 340 in a third embodiment. In FIG. 10, (A) is a diagram illustrating an example of a constitution of a case in which the latch module 1 described above includes one antenna 140. In this case, the radio waves received by the antenna 140 is converted into DC electric power by the power conversion circuit 110 and input to the control circuit 120.

The control circuit 120 controls the switch 130 from a non-conduction state to a conduction state. In the case of this example, the control circuit 120 cannot control the switch 130 from a conduction state to a non-conduction state.

In FIG. 10, (B) is a diagram illustrating an example of a constitution in a case in which the latch module 1 includes two antennas (a first antenna 240 and a second antenna 340). In this case, the latch module 1 includes the first antenna 240, a first power conversion circuit 210, the second antenna 340, a second power conversion circuit 310, and a control circuit 220.

In this example, the first antenna 240 and the second antenna 340 may be provided at different angles from each other.

The first antenna 240 is provided to be able to receive first radio waves in a first direction.

The first power conversion circuit 210 includes a first power input terminal 211 and a first DC power output terminal 212. The first power input terminal 211 is connected to the first antenna 240. The first DC power output terminal 212 is connected to the control circuit 220.

The electric power obtained by the first radio waves received by the first antenna 240 is input to the first power input terminal 211. If the electric power is input to the first power input terminal 211, the first power conversion circuit 210 converts the electric power input to the first power input terminal 211 into DC electric power. The first power conversion circuit 210 outputs DC electric power from the first DC power output terminal 212.

The second antenna 340 is provided to be able to receive second radio waves in a second direction different from the first direction.

The second power conversion circuit 310 includes a second power input terminal 311 and a second DC power output terminal 312. The second power input terminal 311 is connected to the second antenna 340. The second DC power output terminal 312 is connected to the control circuit 220.

The electric power obtained by the second radio waves received by the second antenna 340 is input to the second power input terminal 311. If the electric power is input to the second power input terminal 311, the second power conversion circuit 310 converts the electric power input to the second power input terminal 311 into DC electric power. The second power conversion circuit 310 outputs DC electric power from the second DC power output terminal 312.

The control circuit 220 includes, as input/output terminals, a first input terminal 221, a second input terminal 225, and an output terminal 222.

The first input terminal 221 is connected to the first DC power output terminal 212 of the first power conversion circuit 210. The second input terminal 225 is connected to the second DC power output terminal 312 of the second power conversion circuit 310. The output terminal 222 is connected to the switch 130 and controls the connection state of the switch 130.

The control circuit 220 controls the connection state of the switch 130 to be in a conduction state when the first power conversion circuit 210 outputs DC electric power due to the reception of the first radio waves by the first antenna 240. The control circuit 220 controls the connection state of the switch 130 to be in a non-conduction state when the second power conversion circuit 310 outputs DC electric power due to the reception of the second radio waves by the second antenna 340.

In this way, in the example illustrated in (B) of FIG. 10, the control circuit 220 can not only control the switch 130 from a non-conduction state to a conduction state, but also control the switch 130 from a conduction state to a non-conduction state.

FIG. 11 is a diagram illustrating an example of the first antenna 240 and the second antenna 340 in the third embodiment.

In FIG. 11, (A) is a diagram illustrating an example of an electric field antenna 500 in the third embodiment. (A) illustrates an example of a type of antenna when the first antenna 240 or the second antenna 340 is the electric field antenna 500.

When the first antenna 240 or the second antenna 340 is the electric field antenna 500, the first antenna 240 or the second antenna 340 may be a dipole antenna 501, a monopole antenna 502, an inverted F antenna 503, a meander line antenna 504, or a chip antenna 505.

In FIG. 11, (B) is a diagram illustrating an example of a magnetic field antenna 600 in the third embodiment. In FIG. 11, (B) illustrates an example of a type of antenna when the first antenna 240 or the second antenna 340 is the magnetic field antenna 600.

When the first antenna 240 or the second antenna 340 is the magnetic field antenna 600, the first antenna 240 or the second antenna 340 may be a loop antenna 601.

The types of antennas of the first antenna 240 and the second antenna 340 in this embodiment are not limited to the types of antennas illustrated in (A) and (B) of FIG. 11. In addition, various antennas can be selected as the first antenna 240 and the second antenna 340.

FIG. 12 is a diagram illustrating an example of a constitution of a latch module 1 g in the third embodiment. The latch module 1 g illustrated in FIG. 6 is a modified example of the latch module 1 in the first embodiment. A constituent element in this example that is the same as the latch module 1 described above will be denoted by the same reference numeral and a description thereof will be omitted.

In FIG. 6, the latch module 1 g includes a latch circuit 10 g, a power supply 50, and a load 60.

The latch circuit 10 g includes an electric field antenna 500 a, a magnetic field antenna 600 a, a first power conversion circuit 210 a, a second power conversion circuit 310 a, a control circuit 220, and a switch 130. The electric field antenna 500 a is an example of a first antenna 240 and the magnetic field antenna 600 a is an example of a second antenna 340.

The first power conversion circuit 210 a may include an RF-DC conversion circuit 213 a and a booster circuit 214 a and the second power conversion circuit 310 a may include an RF-DC conversion circuit 313 a and a booster circuit 314 a.

The electric field antenna 500 a receives first radio waves in a first direction. The electric power when the electric field antenna 500 a receives the first radio waves is input to the first power input terminal 211 a of the first power conversion circuit 210 a. The first power conversion circuit 210 a converts the input electric power into DC electric power and outputs the converted DC electric power to the first DC power output terminal 212 a.

In this case, since the magnetic field antenna 600 a is installed to be able to receive second radio waves in a second direction different from the first direction, the magnetic field antenna 600 a does not receive the first radio waves. Therefore, DC electric power is input to only the first input terminal 221 of the control circuit 220.

The magnetic field antenna 600 a receives the second radio waves in the second direction. Electric power when the magnetic field antenna 600 a receives the second radio waves is input to the second power input terminal 311 a of the second power conversion circuit 310 a. The second power conversion circuit 310 a converts the input electric power into DC electric power and outputs the converted DC electric power to the second DC power output terminal 312 a.

In this case, since the electric field antenna 500 a is installed to be able to receive the first radio waves in the first direction different from the second direction, the electric field antenna 500 a does not receive the second radio waves. Therefore, DC electric power is input to only the second input terminal 225 of the control circuit 220.

In this example, the control circuit 220 includes a flip-flop 227. The flip-flop 227 switches a control signal outputs from the output terminal 222 on the basis of a potential of the first input terminal 221 and a potential of the second input terminal 225.

Specifically, the flip-flop 227 is an SR flip-flop (SR-F/F). More specifically, the first input terminal 221 is connected to an S terminal of the flip-flop 227, the second input terminal 225 is connected to an R terminal of the flip-flop 227, and the output terminal 222 is connected to a Q terminal.

In a state in which the electric field antenna 500 a receives the first radio waves, the first power conversion circuit 210 a outputs DC electric power. The output DC electric power is input to the S terminal in which a potential according to the DC electric power corresponds to that of the first input terminal 221 of the flip-flop 227. When the input potential exceeds a threshold value voltage in which a state of the flip-flop 227 is caused to be changed, that is, if a high level is input to the S terminal of the flip-flop 227, the Q terminal of the flip-flop 227 outputs a high level. In this state, the switch 130 is controlled to be in a conduction state. If the switch 130 is controlled to be in the conduction state, the power supply 50 supplies electric power to the load 60.

In a state in which the magnetic field antenna 600 a receives the second radio waves, the second power conversion circuit 310 a outputs DC electric power. The output DC electric power is input to the R terminal in which a potential according to the DC electric power corresponds to that of the second input terminal 225 of the flip-flop 227. When the input potential exceeds a threshold value voltage in which a state of the flip-flop 227 is caused to be changed, that is, if a high level is input to the R terminal of the flip-flop 227, the Q terminal of the flip-flop 227 outputs a low level. In this state, the switch 130 is controlled to be in a non-conduction state.

Electric power is supplied from the power supply 50 to the control circuit 220 including the flip-flop 227. Therefore, in a state in which both of the electric field antenna 500 a and the magnetic field antenna 600 a do not receive radio waves, the flip-flop 227 continues to keep an output state of the Q terminal. That is to say, a connection state of the switch 130 differs depending on whether it is controlled to be in a conduction state or in a non-conduction state in accordance with whether the electric field antenna 500 a or the magnetic field antenna 600 a finally receives radio waves. If the switch 130 is controlled to be in the non-conduction state, the power supply 50 stops the supply of electric power to the load 60.

In this example, since the flip-flop 227 is connected to the power supply 50 via a power supply terminal 223, a constitution in which the flip-flop 227 with low power consumption is selected to significantly minimize an influence on a battery lifespan may be provided. For example, a flip-flop with low power consumption of less than 1 μA (microampere) may be selected.

Also, the control circuit 220 may be composed of a low power consumption latch circuit having a function equivalent to that of a flip-flop.

FIG. 13 is a diagram illustrating a first modified example of the constitution of the latch module 1 in the third embodiment. A latch module 1 h illustrated in FIG. 7 is a modified example of the latch module 1 g described above. A constituent element in this example that is the same as the latch module 1 g will be denoted by the same reference symbol and a description thereof will be omitted. The latch module 1 h has a constitution different from that of the latch module 1 g in that a power detector 226 is included in a control circuit 220 and a flip-flop 227 is not included.

A constitution of the control circuit 220 included in the latch module 1 h is the same as that of the control circuit 120 b illustrated in FIG. 3. That is to say, a constitution of the power detector 226 included in the control circuit 220 is the same as that of the power detector 126 illustrated in FIG. 4.

In the example associated with the latch module 1 h, a first DC power output terminal 212 a of a first power conversion circuit 210 a is connected to a first input terminal 221 of the control circuit 220. That is to say, when an electric field antenna 500 a receives first radio waves, a current proportional to electric power due to the received radio waves is input to a detection input terminal 2261 of the power detector 226. In this case, when a potential proportional to the current input to an input terminal 2261 is higher than a reference input potential VDET in the power detector 226, a high level is output to a voltage detection output terminal 2263 and a switch 130 is controlled to be in a conduction state.

Also, a second DC power output terminal 312 a of a second power conversion circuit 310 a is connected to a second input terminal 225 of the control circuit 220. That is to say, when a magnetic field antenna 600 a receives second radio waves, a current proportional to the electric power obtained by the received radio waves is input to a reference input terminal 2262 of the power detector 226. In the power detector 226, a current amplifier is present in the next stage of an input terminal 2262. A current input to the reference input terminal 2262 is amplified to be doubled using the current amplifier. Furthermore, a current adder in the next stage subtracts a current input to the reference input terminal 2262 from a current input to the detection input terminal 2261. When a potential proportional to the current which has passed through the current adder is lower than the reference input potential VDET in the power detector 226, a low level is output to the voltage detection output terminal 2263 and the switch 130 is controlled to be in a non-conduction state.

In this way, the latch module 1 h including the control circuit 220 having the power detector 226 operates in the same manner as in the latch module 1 g including the control circuit 220 a having the flip-flop 227.

When the latch module 1 h includes the power detector 226 in the control circuit 220, it is possible to further reduce power consumption as compared with the latch module 1 g.

FIG. 14 is a diagram illustrating a second modified example of the constitution of the latch module 1 in a third embodiment. A latch module 1 i illustrated in FIG. 14 is a modified example of the latch module 1 g described above. A constituent element in the second modified example that is the same as the latch module 1 g will be denoted by the same reference symbol and a description thereof will be omitted. The latch module 1 i has a different constitution from the latch module 1 g in that an electric field antenna 500 is used for both a first antenna 240 and a second antenna 340.

In the example illustrated in FIG. 14, the electric field antenna 500 b (the first antenna 240) and the electric field antenna 500 c (the second antenna 340) are provided at different positions from each other. That is to say, in the latch module 1 i, installation positions of the antennas are different from each other. Each of the installation positions is a position in the latch module 1 i in which the antenna is installed.

The electric field antenna 500 b is installed to be able to receive first radio waves in a first direction. The electric field antenna 500 c is installed to be able to receive second radio waves in a second direction different from the first direction.

FIG. 15 is a diagram illustrating a second modified example of the constitution of the latch module 1 in the third embodiment. A latch module 1 j illustrated in FIG. 15 is a third modified example of the latch module 1 i described above. A constituent element in this example that is the same as the latch module 1 i will be denoted by the same reference symbol and a description thereof will be omitted. The latch module 1 j has a constitution different from that of the latch module 1 i in that installation angles of the first antenna 240 and the second antenna 340 are different from each other.

In this example illustrated in FIG. 15, the latch module 1 j includes an electric field antenna 500 d and an electric field antenna 500 e. The electric field antenna 500 d is an example of the first antenna 240 and the electric field antenna 500 e is an example of the second antenna 340.

In the example illustrated in FIG. 15, the electric field antenna 500 b (the first antenna 240) and the electric field antenna 500 c (the second antenna 340) are provided at different angles. That is to say, since the first radio waves and the second radio waves are provided at different angles, the first radio waves and the second radio waves do not interfere with each other.

As an example, the electric field antenna 500 b (the first antenna 240) and the electric field antenna 500 c (the second antenna 340) may be provided perpendicular to each other.

FIG. 16 is a diagram illustrating a fourth modified example of the constitution of the latch module 1 in the third embodiment.

In FIG. 16, (B) is a diagram illustrating the arrangement of an antenna 701 and an antenna 702 using a two-dimensional Cartesian coordinate system of an x axis and a y axis. The antenna 701 illustrated in FIG. 9 is an example of the first antenna 240 described above and the antenna 702 is an example of the second antenna 340 described above. Hereinafter, when the antenna 701 and the antenna 702 are equivalent, the antenna 701 and the antenna 702 are referred to as an “antenna 700.” The antenna 700 is an example of the electric field antenna 500.

The antenna 701 is arranged along the x axis, and the antenna 702 is arranged along the y axis. In this example, the antenna 701 and the antenna 702 are arranged at different angles from each other.

In FIG. 16, (B) is a diagram illustrating the arrangement of the antenna 701 and the antenna 702 using a three-dimensional Cartesian coordinate system of an x axis, a y axis, and a z axis. In (B) of FIG. 16, the arrangement of the antenna 701 and the antenna 702 illustrated using the two-dimensional Cartesian coordinate system of the x axis and the y axis in (A) of FIG. 16 is illustrated in a three-dimensional space.

The antenna 701 and the antenna 702 are accommodated in a housing 703. Furthermore, the antenna 701 and the antenna 702 are arranged in the same plane. When the antenna 701 and the antenna 702 are arranged at different angles from each other as illustrated in (B) of FIG. 16, even when the antenna 701 and the antenna 702 are arranged on the same plane, the first radio waves and the second radio waves do not interfere with each other.

FIG. 17 is a diagram illustrating a fifth modified example of the constitution of the latch module 1 in the third embodiment. A latch module 1 k illustrated in FIG. 10 is a modified example of the latch module 1 j described above. A constituent element in this example that is the same as the latch module 1 j will be denoted by the same reference symbols and a description thereof will be omitted. The latch module 1 k has a constitution different from that of the latch module 1 j in that, although the installation angles of the first antenna 240 and the second antenna 340 are the same, the first antenna 240 and the second antenna 340 include the dipole antennas 501 having different lengths from each other.

In the example illustrated in FIG. 17, the latch module 1 k includes an electric field antenna 500 f and an electric field antenna 500 g. The electric field antenna 500 f is an example of the first antenna 240 and the electric field antenna 500 g is an example of the second antenna 340.

In this example, the electric field antenna 500 f and the electric field antenna 500 g includes antennas having lengths different from each other. In order to minimize the interference between the first radio waves and the second radio waves, the length of the electric field antenna 500 f and the length of the electric field antenna 500 g are selected on the basis of frequency of the radio waves. For example, the length of the electric field antenna 500 f and the length of the electric field antenna 500 g are preferably ½ or ¼ of wavelengths λ of the radio waves received by the antennas. In this case, the electric field antenna 500 f and the electric field antenna 500 g can efficiently receive radio waves without generating reflected waves.

Specifically, when the frequency of the first radio waves is 2.4 GHz and the frequency of the second radio waves is 5 GHz, a wavelength of the first radio waves is about 12.5 cm and a wavelength of the second radio waves is about 6 cm. Furthermore, when a dipole antenna with a wavelength of λ/2 is utilized, in each antenna, a length of the antenna configured to receive the first radio waves is 6.25 cm and a length of the antenna configured to receive the second radio waves is 3 cm.

As described above, when a constitution in which a latch module 1 k in which the dipole antenna 501 having an antenna length of ½ of the wavelengths λ of the first radio waves and the second radio waves of different wavelengths is utilized is provided, it is possible to minimize interference between the first radio waves and the second radio waves. In this case, one of the radio waves can be used for turning on the switch 130 and the other of the radio waves can be used for turned off the switch 130.

Although a case in which a length of the first antenna 240 and a length of the second antenna 340 are different has been described using an example of the dipole antenna 501, the same applies not only to an example of the dipole antenna 501, but also to the monopole antenna 502, the inverted F antenna 503, the meander line antenna 504, and the chip antenna 505. Similarly, these antennas may be configured so that a length of the antenna included in the first antenna 240 and a length of the antenna included in the second antenna 340 are different.

FIG. 18 is a diagram illustrating an example of a housing having a waterproof structure in the third embodiment. As illustrated in FIG. 11, a latch waterproof module 2 b includes a latch circuit 101, a power supply 50 configured to output DC electric power, a load 60 driven by DC electric power supplied from the power supply 50, and a housing 80.

The housing 80 includes the latch circuit 101, the power supply 50, and the load 60 accommodated therein. The housing 80 has waterproof performance.

Summary of Effects of Third Embodiment

According to the embodiment described above, the latch module 1 switches a connection state of the switch 130 by detecting the first radio waves received by the first antenna 240 and the second radio waves received by the second antenna 340. The latch module 1 can switch the switch 130 from a non-conduction state to a conduction state when configured in this way. Furthermore, the latch module 1 can switch the switch 130 from a conduction state to a non-conduction state.

Also, according to the above-described embodiment, the first antenna 240 and the second antenna 340 are provided at different positions from each other. Therefore, the latch module 1 can prevent the first radio waves in the first direction and the second radio waves in the direction different from the first direction from interfering with each other. That is to say, it is possible to prevent malfunction.

Furthermore, according to the above-described embodiment, the first antenna 240 and the second antenna 340 are provided at different angles from each other. Therefore, the latch module 1 can prevent the first radio waves in the first direction and the second radio waves in the direction different from the first direction from interfering with each other. That is to say, it is possible to prevent malfunction.

In addition, according to the above-described embodiment, the first antenna 240 and the second antenna 340 are provided perpendicular to each other. Therefore, according to the above-described embodiment, it is possible to prevent the first radio waves and the second radio waves from interfering with each other. That is to say, it is possible to prevent malfunction.

Moreover, according to the above-described embodiment, the first antenna 240 is the electric field antenna 500 and the second antenna 340 is the magnetic field antenna 600. Therefore, it is possible to prevent the first radio waves and the second radio waves from interfering with each other. That is to say, it is possible to prevent malfunction.

Fourth Embodiment

A fourth embodiment of the present invention will be described below with reference to the drawings.

FIG. 19 is a diagram illustrating an example of a constitution of a latch system 100 in the fourth embodiment. In FIG. 19, a latch module 1 m includes a first antenna 740 a, a second antenna 740 b, a first power conversion circuit 710 a, a second power conversion circuit 710 b, a control circuit 720, a switch 130, a power supply 50, and a load 60. The first power conversion circuit 710 a may include an RF-DC conversion circuit 713 a and a booster circuit 714 a and the second power conversion circuit 710 b may include an RF-DC conversion circuit 713 b and a booster circuit 714 b.

The first antenna 740 a is provided to be able to receive radio waves. The second antenna 740 b is provided to be able to receive radio waves and has the same characteristics and gain as in the first antenna 740 a. The first antenna 740 a and the second antenna 740 b are arranged distance from each other at a prescribed distance.

In this example, a transmission point T1 indicates a point far distance from a point in which the first antenna 740 a is provided and a point in which the second antenna 740 b is provided. Specifically, the antennas are installed at locations in which the radio waves transmitted from the transmission point T1 are in a far field.

Radio waves are divided into a far field and a near field in accordance with a distance from the transmission point. For example, a boundary position between a far field and a near field is represented by λ/2π using a wavelength λ of radio waves. As an example, at 2.4 GHz, about 2 cm from a transmission point is a boundary between a far field and a near field.

Since radio waves can be regarded as plane waves in a far field, if distances from a transmission point are the same, an electric field intensity and a magnetic field intensity are the same. An intensity is inversely proportional to the first power of distance.

On the other hand, in a near field, in an electric field antenna, an electric field intensity is inversely proportional to the third power of distance and a magnetic field intensity is inversely proportional to the second power of distance. In addition, in a magnetic field antenna, an electric field intensity is inversely proportional to the second power of distance and a magnetic field intensity is inversely proportional to the third power of distance. That is to say, an electric field intensity and a magnetic field intensity in a near field have a significantly larger change in intensity depending on a distance than in a far field.

When radio waves from a far field is received, the radio waves seen from the first antenna 740 a and the second antenna 740 b are plane waves and magnitudes of electric powers P1 and P2 received by the antennas are substantially the same.

In this embodiment, the first antenna 740 a and the second antenna 740 b have the same characteristics and gain. Thus, when each of the first antenna 740 a and the second antenna 740 b receives radio waves from the transmission point T1, the DC electric power output by the first power conversion circuit 710 a and the DC electric power output by the second power conversion circuit 710 b are substantially the same.

In this example, radio waves from a far field are regarded as noise. The radio waves from the far field are radio waves floating in the environment. For example, when the latch module 1 m receives the radio waves from the far field, a malfunction in which a connection state of the switch 130 is switched is likely to be caused.

The first power conversion circuit 710 a includes a first power input terminal 711 a to which electric power obtained when the first antenna 740 a receives radio waves input and a first DC power output terminal 712 a configured to output DC electric power, converts electric power input to the first power input terminal 711 a into DC electric power and outputs the converted DC electric power from the first DC power output terminal 712 a.

The second power conversion circuit 710 b includes a second power input terminal 711 b to which electric power obtained when the second antenna 740 b receives radio waves is input and a second DC power output terminal 712 b configured to output DC electric power, converts electric power input to the second power input terminal 711 b into DC electric power, and outputs the converted DC electric power from the second DC power output terminal 712 b.

The control circuit 720 includes a first input terminal 721 connected to the first DC power output terminal 712 a of the first power conversion circuit 710 a, a second input terminal 725 connected to the second DC power output terminal 712 b of the second power conversion circuit 710 b, an output terminal 722 connected to the switch 130 and configured to control a connection state of the switch 130, and a power supply terminal 723.

The power supply terminal 723 of the control circuit 720 is connected to the power supply 50. The load 60 is connected to the power supply 50 via the switch 130.

The control circuit 720 switches a connection state of the switch 130 in accordance with the result of comparing the electric power input to the first input terminal 721 with the electric power input to the second input terminal 725.

FIG. 20 is a diagram illustrating a case in which the first antenna 740 a receives radio waves having an intensity higher than that of the second antenna 740 b in an example of the constitution of the latch system 100 in the fourth embodiment. A constituent element in this case that is the same as the latch module 1 m described above will be denoted by the same reference symbol and a description thereof will be omitted.

In this example, a transmission point T2 is located in a near field of the first antenna 740 a. In the near field, a change in electric field intensity and magnetic field intensity depending on a distance is large. Thus, the electric power due to the radio waves received by the first antenna 740 a is significantly different from the electric power due to the radio waves received by the second antenna 740 b.

For example, if radio waves are transmitted in the vicinity of the first antenna 740 a, an electric field intensity and a magnetic field intensity in the vicinity of the second antenna 740 b are significantly attenuated with respect to an electric field intensity and a magnetic field intensity in the vicinity of the first antenna 740 a.

When the transmission point T2 is located in the near field of the first antenna 740 a, the electric power due to the radio waves received by the first antenna 740 a is significantly different from the electric power due to the radio waves received by the second antenna 740 b. Thus, the DC electric power output by the first power conversion circuit 710 a is significantly different from the DC electric power output by the second power conversion circuit 710 b. That is to say, the electric power input to the first input terminal 721 of the control circuit 720 is significantly different from the electric power input to the second input terminal 725.

The control circuit 720 switches a connection state of the switch 130 in accordance with the result of comparing the electric powers input to the first input terminal 721 and the second input terminal 725. Thus, when the transmission point T2 is located in the near field of the first antenna 740 a, a connection state of the switch 130 is switched.

For example, when the electric power input to the first input terminal 721 is electric power which is twice or more the electric power input to the second input terminal 725, the control circuit 720 controls the switch 130 to be in a conduction state.

FIG. 21 is a diagram illustrating a case in which the second antenna 740 b receives radio waves having an intensity higher than that of the first antenna 740 a in an example of the constitution of the latch system 100 in the fourth embodiment. A constituent element in this case that is the same as the latch module 1 m described above will be denoted by the same reference symbol and a description thereof will be omitted.

In this example, a transmission point T3 is located in a near field of the second antenna 740 b. If radio waves are transmitted from the transmission point T3 near the second antenna 740 b, an electric field intensity and a magnetic field intensity in the vicinity of the first antenna 740 a are significantly attenuated with respect to an electric field intensity and a magnetic field intensity in the vicinity of the second antenna 740 b.

For example, when the electric power input to the second input terminal 725 is larger than the electric power input to the first input terminal 721 by a prescribed amount or more, the control circuit 720 controls the switch 130 to be in a non-conduction state.

As illustrated in FIGS. 20 and 21, when radio waves in a near field are transmitted near either the first antenna 740 a or the second antenna 740 b, the latch circuit 10 can detect a position of a transmitter and it is possible to switch a connection state of the switch 130 without a malfunction.

FIG. 22 is a diagram illustrating an example of a constitution of the control circuit 720 in the fourth embodiment.

In FIG. 22, (A) is a diagram illustrating an example of a circuit constitution of the control circuit 720 of the fourth embodiment. As illustrated in (A) of FIG. 22, the control circuit 720 is constituted of a power detector 726 and a feedback resistor 724. The power detector 726 includes a first input terminal 7212, a second input terminal 7252, and the output terminal 7222 as input/output terminals. The power detector 726 has the output terminal 7222 connected to the first input terminal 7212 via the feedback resistor 724. The feedback resistor 724 feeds back the electric power of the output terminal 7222 of the power detector 726 to an input terminal 7212. For this reason, if the output terminal 7222 is a high level, the power detector 726 maintains a high level of an output terminal 7212 unless a large amount of electric power is input to the second input terminal 7252 to make the switch 130 non-conduction. The power detector 726 includes a current amplifier 7261, a current adder 7262, and an current comparator 7263 as constituent elements. The power detector 726 compares the electric powers input to the first input terminal 7212 and the second input terminal 7252 by comparing the currents input as values proportional to the electric powers input to the first input terminal 7212 and the second input terminal 7252.

The current amplifier 7261 amplifies a current I_(INM) input to the second input terminal 7252. In this example, the current amplifier 7261 amplifies the current input to the second input terminal 7252 G times.

The current adder 7262 adds a current (G×T_(INM)) obtained by amplifying a current (G×I_(INM)) input to the second input terminal 7252 G times using the current amplifier 7261 and a current I_(INP) input to the first input terminal 7212. The current adder 7262 outputs the added current.

The current comparator 7263 compares the current (I_(NP)−G×I_(INM)) output as a result of addition by the current adder 7262 with the detected current I_(DET). The current comparator 7263 outputs a voltage corresponding to the comparison result to the output terminal 7222.

To be specific, the current comparator 7263 outputs a high level when the current output as a result of addition by the current adder 7262 is the detected current I_(DET) or more and outputs a low level when the current output as a result of addition by the current adder 7262 is less than the detected current I_(DET). Hereinafter, the current comparator 7263 is also be referred to as a “comparator.”

That is to say, the current comparator 7263 outputs a high level when a difference between a current flowing through the first input terminal 7212 and a current obtained by amplifying a current flowing through the second input terminal 7252 G times using the current amplifier 7261 is the detected current I_(DET) or more. Furthermore, the current comparator 7263 outputs a low level when a difference between a current flowing through the first input terminal 7212 and a current obtained by amplifying a current flowing through the second input terminal 7252 G times using the current amplifier 7261 is less than the detected current I_(DET).

For example, when a gain (an amplification factor) of the current amplifier 7261 is set to a gain (an amplification factor) which is twice the gain (the amplification factor), the current comparator 7263 does not output a high level unless the current flowing through the first input terminal 7212 is a value or more obtained by adding the detected current I_(DET) to a current obtained by doubling the current flowing through the second input terminal 7252.

Hereinafter, a state in which the current comparator 7263 outputs a low level to the output terminal 7222 is also referred to as an “off state” and a state in which the current comparator 7263 outputs a high level to the output terminal 7222 is also referred to as an “on state.”

In FIG. 22, (B) is a table showing a correspondence relationship between a current input to the power detector 726 and an output potential.

When an current value obtained by subtracting a current obtained by amplifying the current flowing through the second input terminal 7252 G times from the current flowing through the first input terminal 7212 is the detected current I_(DET) or more, the output terminal 7222 outputs a high level. Since the output terminal 7222 is connected to the switch 130, in this case, the control circuit 720 controls the switch 130 to be in a conduction state.

When an current value obtained by subtracting the current obtained by amplifying the current flowing through the second input terminal 7252 G times from the current flowing through the first input terminal 7212 is less than the detected current I_(DET), the output terminal 7222 outputs a low level. Since the output terminal 7222 is connected to the switch 130, in this case, the control circuit 720 controls the switch 130 to be in a non-conduction state.

FIG. 23 is a diagram illustrating an example of a constitution of the power detector 726 a having gain (amplification factor) switching in the fourth embodiment. The power detector 726 a is an example of the power detector 726. A constituent element in this example that is the same as the power detector 726 will be denoted by the same reference numeral and a description thereof will be omitted.

An example of a case in which the power detector 726 a switches a gain will be described with reference to FIG. 23. As an example, a case in which, when the power detector 726 a is in an off state, a gain is doubled to prevent a malfunction, whereas when the power detector 726 a is in an on state, a gain is set to a gain which is ½ times the gain so that it is difficult to shift to an off state will be described.

In this example, the power detector 726 a includes a gain switch 7264.

When the second input terminal 7252 of the power detector 726 a is connected to the current amplifier 7261, the current flowing through the second input terminal 7252 can obtain the doubled gain.

When the power detector 726 a is in an off state and receives radio waves transmitted from a far field, the currents input to the first input terminal 7212 and the second input terminal 7252 are substantially the same. Thus, a current of the second input terminal 7252 having the doubled gain becomes larger and a potential of the output terminal 7222 is maintain in an off state. That is to say, when the latch module 1 m includes the power detector 726 a, it is possible to prevent a malfunction.

On the other hand, when the power detector 726 a receives radio waves in a near field to be in an on state, the power detector 726 a can be maintained in a state by performing setting so that the current I_(INP) flowing through the first input terminal 7212 is larger than the current I_(INM) flowing through the second input terminal 7252.

For example, if the gain (amplification factor) connected to the second input terminal 7252 is changed from 2 times to ½, even if the current input to the first input terminal 7212 and the current input to the second input terminal 7252 are substantially the same, the current flowing through the first input terminal 7212 becomes larger. Thus, it becomes difficult for the power detector 726 a to shift to an off state. That is to say, the latch module 1 m can be easily maintained in the on state.

FIG. 24 is a diagram illustrating an example of the circuit constitution of the power detector 726 a having the gain switching in the fourth embodiment. A constituent element in this example that is the same as the power detector 126 described in the first embodiment will be denoted by the same reference numeral and a description thereof will be omitted. In FIG. 24, the power detector 726 a further includes a current amplifier 7261, a current adder 7262, and a gain switch 7264.

The current amplifier 7261 includes a transistor Q5 and a transistor Q6. Both of the transistor Q5 and the transistor Q6 are n-channel type transistors. The transistor Q5 has a source connected to a ground point TG, a gate connected to a drain of the transistor Q5 and a gate of the transistor Q6, and the drain connected to the second input terminal 7252. The transistor Q6 has a source connected to the ground point TG, the gate connected to the gate of the transistor Q5, and a drain connected to the current adder 7262. The transistor Q5 and the transistor Q6 constitute a current mirror circuit. The current I_(INM) input to the second input terminal 7252 flows between the drain and the source of the transistor Q5 as a current I1. In this example, ½×I1 flows between the drain and the source of the transistor Q6 as a current I2.

The gain switch 7264 includes a transistor Q7 and a transistor Q8. The transistor Q7 is an n-channel type transistor and the transistor Q8 is a p-channel type transistor.

The transistor Q7 has a source connected to the ground point TG, a gate connected to the gate of the transistor Q6, and a drain connected to a drain of the transistor Q8.

The transistor Q8 has a source connected to a connection point between the drain of the transistor Q6 and the current adder 7262, a gate connected to the output terminal 7222, and the drain connected to the drain of the transistor Q7. In this example, 3/2×I1 flows between the drain and the source of the transistor Q7 as a current I3.

The gain switch 7264 switches a current value of the current flowing through the current adder 7262 by controlling the current I3 in accordance with the state of the output terminal 7222.

When the output terminal 7222 is in a low level, the current I3 flows between the source and the drain of the transistor Q8. In this case, since I2+I3 (that is, ½×I1+3/2×I1=2×I1) flows through the current adder 7262, the gain is doubled.

When the output terminal 7222 is in a high level, a current does not flow between the source and the drain of the transistor Q8. In this case, since 12 (that is, ½×I1+3/2×I1=2×I1) flows through the current adder 7262, the gain is halved.

Here, a current flowing between a drain and a source of a MOS transistor is proportional to a gate width W and inversely proportional to a gate length L.

A value of the gain of the power detector 726 a is arbitrarily adjusted using the gate width W and the gate length L of the MOS transistor constituting the transistor Q6 and the transistor Q7.

FIG. 25 is a diagram illustrating an example of a housing 80 with a waterproof structure in the fourth embodiment. As illustrated in FIG. 25, a latch waterproof module 2 c includes a latch circuit 10 p, a power supply 50 configured to output DC electric power, a load 60 driven through DC electric power supplied from the power supply 50, and the housing 80.

The housing 80 includes the latch circuit 10 p, the power supply 50, and the load 60 accommodated therein. The housing 80 has waterproof performance.

Summary of Effects of Fourth Embodiment

According to the embodiment described above, the latch module 1 m includes the first antenna 740 a and the second antenna 740 b having the same characteristics and gain as in the first antenna 740 a. The control circuit 720 compares the electric power due to the radio waves received by the first antenna 740 a with the electric power due to the radio waves received by the second antenna 740 b.

When a difference between the electric power due to the radio waves received by the first antenna 740 a and the electric power due to the radio waves received by the second antenna 740 b is less than a prescribed value, the transmission point of radio waves is conceivable to be in a far field. Thus, the control circuit 720 does not switch the connection state of the switch 130. When a difference between the electric power due to the radio waves received by the first antenna 740 a and the electric power due to the radio waves received by the second antenna 740 b is a prescribed value or more, the transmission point of radio waves is conceivable to be in a near field. Thus, the control circuit 720 switches the connection state of the switch 130.

Therefore, the latch module 1 m can detect that the noise radio waves from the far field is not near the transmitter regardless of the intensity of radio waves and can prevent a malfunction due to the radio waves from the far field.

Also, since these controls utilize the electric field characteristics of the transmission radio waves, power consumption of the battery of the circuit does not occur for detection.

Furthermore, according to the above-described embodiment, the control circuit 720 switches the connection state of the switch 130 to a conduction state when the electric power input from the first input terminal 721 is larger than the electric power input from the second input terminal 725 and switches the connection state of the switch 130 to a non-conduction state when the electric power input from the first input terminal 721 is smaller than the electric power input from the second input terminal 725.

Therefore, when the latch module 1 m includes the control circuit 720, it is possible to switch the power supply 50 and the load 60 between a conduction state and a non-conduction state.

Furthermore, according to the above-described embodiment, the control circuit 720 includes the power detector 726. Therefore, the control circuit 720 including the power detector 726 can maintain the state of the switch 130 with low power consumption.

In addition, according to the above-described embodiment, when the power detector 726 includes the current amplifier 7261, in a case in which there is a difference between the electric power input to the first input terminal 7212 and the electric power input to the second input terminal 7252, the connection state of the switch 130 is switched.

The connection state of the switch 130 is switched only when a difference of a prescribed value or more set using the gain of the current amplifier 7261 is detected. Thus, the power detector 726 can prevent a malfunction.

Moreover, according to the above-described embodiment, the power detector 726 a can switch the gain when including the gain switch 7264. It is possible to switch the gain between when the power detector 726 a is in the on state and when the power detector 726 a is in the off state.

In a state in which the power detector 726 a is in the off state, when the power detector 726 a increases a weight of the gain, the power detector 726 a can be easily maintained in the off state and can prevent a malfunction.

In a case in which the power detector 726 a is in the on state, when the power detector 726 a reduces a weight of the gain, the power detector 726 a can be easily maintained in the on state.

According to the above-described embodiment, the first antenna 740 a and the second antenna 740 b are arranged distance from each other at a prescribed distance. The latch module 1 m switches the connection state of the switch 130 when the transmitter 70 is brought closer to the first antenna 740 a or the second antenna 740 b.

Therefore, the position in which the transmitter 70 is brought closer to the antenna to make the connection state of the switch 130 conductive is different from the position in which the transmitter 70 is brought closer to the antenna to make the connection state of the switch 130 non-conduction. Thus, it is possible to prevent a malfunction.

While the embodiments of the present invention have been described in detail above with reference to the drawings, the specific constitution is not limited to the embodiments and designs and the like within a range that does not depart from the gist of the present invention are also included. Furthermore, while the operation has been described from a current according to the electric power using the radio waves received by the antennas in the embodiments of the present invention, the operation may be described from a voltage according to the electric power using the radio waves received by the antennas. 

What is claimed is:
 1. An electronic circuit, comprising: a switch which is connected between a power supply configured to output direct current (DC) electric power and a load driven by DC electric power supplied from the power supply and which switches a connection state between the power supply and the load from a non-conduction state in which a supply of electric power from the power supply to the load is cut off to a conduction state in which the supply of electric power from the power supply to the load is allowed; a power conversion circuit which includes a power input terminal to which electric power obtained through radio waves received by an antenna capable of receiving radio waves is input and a DC power output terminal configured to output DC electric power and which converts electric power input to the power input terminal into DC electric power and outputs the converted DC electric power from the DC power output terminal; and a control circuit which includes an input terminal connected to the DC power output terminal of the power conversion circuit and an output terminal connected to the switch and configured to control a connection state of the switch and controls the connection state of the switch to be in a conduction state when the power conversion circuit outputs DC electric power due to receiving the radio waves by the antenna, wherein the power conversion circuit includes at least a first capacitor including a first electrode connected to the power input terminal and a second electrode, a first diode having an anode connected to a ground point and a cathode connected to the second electrode of the first capacitor, a second capacitor including a first electrode connected to the DC power output terminal and a second electrode connected to a ground point, and a second diode having an anode connected to the input terminal via a capacitor and a cathode connected to a first electrode of the second capacitor.
 2. The electronic circuit according to claim 1, wherein the power conversion circuit further includes: a third capacitor including a first electrode and a second electrode connected to a ground point; a third diode having an anode connected to a second electrode of the first capacitor and a cathode connected to the first electrode of the third capacitor; a fourth capacitor including a first electrode connected to the power input terminal and a second electrode; and a fourth diode having an anode connected to a connection point between the first electrode of the third capacitor and the cathode of the third diode and a cathode connected to the second electrode of the fourth capacitor.
 3. The electronic circuit according to claim 2, wherein the power conversion circuit further includes: a fifth capacitor including a first electrode and a second electrode connected to a ground point; a fifth diode having an anode connected to the second electrode of the fourth capacitor and a cathode connected to the first electrode of the fifth capacitor; a sixth capacitor including a first electrode connected to the power input terminal and a second electrode; and a sixth diode having an anode connected to a connection point between the first electrode of the fifth capacitor and the cathode of the fifth diode and a cathode connected to the second electrode of the sixth capacitor.
 4. A module, comprising: the electronic circuit according to claim 1; a power supply configured to output DC electric power; and a load driven through DC electric power supplied from the power supply.
 5. The module according to claim 4, wherein the module is accommodated in a waterproof housing.
 6. A system, comprising: the module according to claim 4; and a transmitter configured to transmit prescribed radio waves to the module.
 7. A system, comprising: the module according to claim 5; and a transmitter configured to transmit prescribed radio waves to the module.
 8. A module, comprising: the electronic circuit according to claim 2; a power supply configured to output DC electric power; and a load driven through DC electric power supplied from the power supply.
 9. The module according to claim 8, wherein the module is accommodated in a waterproof housing.
 10. A system, comprising: the module according to claim 8; and a transmitter configured to transmit prescribed radio waves to the module.
 11. A system, comprising: the module according to claim 9; and a transmitter configured to transmit prescribed radio waves to the module.
 12. A module, comprising: the electronic circuit according to claim 3; a power supply configured to output DC electric power; and a load driven through DC electric power supplied from the power supply.
 13. The module according to claim 12, wherein the module is accommodated in a waterproof housing.
 14. A system, comprising: the module according to claim 12; and a transmitter configured to transmit prescribed radio waves to the module.
 15. A system, comprising: the module according to claim 13; and a transmitter configured to transmit prescribed radio waves to the module. 